1. Field of the Invention
The present invention relates to a variable valve actuating mechanism of a four-stroke engine preferably applicable to a vehicle such as a motorcycle, wherein the variable valve actuating mechanism includes a camshaft having a pair of cams for alternate selective use in actuating one engine valve, where the mechanism can selectively use either one of the respective cams for performing an opening/closing operation of the engine valve.
2. Description of the Background Art
Conventionally, it has been known to provide a valve actuating mechanism which includes a cam shaft, a rocker arm shaft arranged in parallel with the cam shaft, and a rocker arm supported on the rocker arm shaft such that the rocker arm is pivotally movable about an axis of the rocker arm shaft and is movable in the axial direction of the rocker arm shaft. In response to the rotational driving of the cam shaft, the rocker arm is brought into contact with either one of the respective cams and is rocked to open or close the engine valve and, at the same time, the rocker arm is suitably moved in the axial direction thus allowing the selective use of either one of the respective cams for performing opening/closing operation of the engine valve as disclosed in Japanese patent document JP-A-2001-20710.
In the above-mentioned conventional technique, the rocker arm is moved in the axial direction using engine oil pressure. However, recently, an engine is requested to quickly respond to an operation demand from a driver to the engine.
The above-mentioned conventional arrangement which moves the rocker arm using the engine oil pressure has a drawback that it is difficult to make the moving time of the rocker arm stable (particularly, to enable the quick movement) attributed to a change of state of an engine oil (a change of the viscosity of the engine oil or the like attributed to an oil temperature change or the like). Further, there also exists a drawback that an oil passage for supplying an oil pressure is necessary around a valve chamber and hence, the arrangement of the valve actuating mechanism per se becomes complicated.